At 6:30 am the smoker temp had dropped to 178. I don't know how long it had been that low but my guess is about an hour. I need a guru.

I had the opposite experience on a Brisket about a year ago. Got cocky with the WSM and went to bed. I checked the meat in the night to find that the side door had fallen off (didn't have it shut completely) and the cooker was running above 300